Why is MySQL not connecting to my app in Android Studio?

Question

I'm working on this homework assignment and trying to connect to a local MySQL database, the app installs and runs in my AVD but when I click the 'get data' button, i'm returned the connError message.

I'm very new at this and want to get into this field, so i've looked up multiple videos and articles, but for some reason I am unable to find a solution to this issue. Here is my main java code.

public class MainActivity extends AppCompatActivity {

    ItemAdapter itemAdapter;
    Context thisContext;
    ListView myListView;
    TextView progressTextView;
    Map<String, Double> fruitsMap = new LinkedHashMap<String, Double>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Resources res = getResources();
        myListView = findViewById(R.id.myListView);
        progressTextView = findViewById(R.id.progressTextView);
        thisContext = this;

        progressTextView.setText("");
        Button btn = findViewById(R.id.getDataBtn);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                GetData retrieveData = new GetData();
                retrieveData.execute("");
            }
        });
    }

    private class GetData extends AsyncTask<String, String, String> {

        String msg = "";
        // JDBC driver name and database URL
        static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
        // Example: 10.20.30.40.3306
        static final String DB_URL = "jdbc:mysql://localhost:3306/fruits" +
                DbStrings.DATABASE_URL + "/" +
                DbStrings.DATABASE_NAME;

        @Override
        protected void onPreExecute() {
            progressTextView.setText("Connecting to database...");
        }

        @Override
        protected String doInBackground(String... params) {

            Connection conn = null;
            Statement stmt = null;

            try {
                Class.forName(JDBC_DRIVER);
                conn = DriverManager.getConnection
                        (DB_URL, DbStrings.USERNAME, DbStrings.PASSWORD);

                stmt = conn.createStatement();
                String sql = "SELECT * FROM fruits";
                ResultSet rs = stmt.executeQuery(sql);

                while (rs.next()) {
                    String name = rs.getString("item");
                    double price = rs.getDouble("price");

                    fruitsMap.put(name, price);
                }

                msg = "Process complete";

                rs.close();
                stmt.close();
                conn.close();


            } catch (SQLException connError) {
                msg = "An exception was thrown for JDBC.";
                connError.printStackTrace();
            } catch (ClassNotFoundException e) {
                msg = "A class not found exception was thrown.";
                e.printStackTrace();
            } finally {
                try {
                    if (stmt != null) {
                        stmt.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                try {
                    if (conn != null) {
                        conn.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            return null;
        }

        @Override
        protected  void  onPostExecute(String msg) {
            progressTextView.setText(this.msg);

            if (fruitsMap.size() > 0) {
                itemAdapter = new ItemAdapter(thisContext, fruitsMap);
                myListView.setAdapter(itemAdapter);
            }
        }
    }

} //End of MainActivity

The expected results should be a database showing of various fruits and their prices in a TextView.

Answer 1

Android does not support MySQL out of the box. The "normal" way to access your database would be to put a Restful server in front of it and use the HTTPS protocol to connect to the Restful front end.

Have a look at ContentProvider. It is normally used to access a local database (SQLite) but it can be used to get data from any data store.

I do recommend that you look at having a local copy of all/some of your websites data locally, that way your app will still work when the Android device hasn't got a connection. If you go down this route then a service can be used to keep the two databases in sync.